In recent years, information processing systems constructed by coupling plural information processing devices by plural switch devices have been used in data centers and so forth. FIG. 34 illustrates one example of an information processing system in a data center. In FIG. 34, S0 to Sn denote transmission-side end nodes and R0 to Rn denote reception-side end nodes. The end node is an information processing device for example. The transmission-side end node is an information processing device that transmits packets and the reception-side end node is an information processing device that receives the packets transmitted by the transmission-side end node.
SW#00 to SW#05 are switch devices that construct a network. SW#00 to SW#02 are switch devices coupled to the end nodes and are called leaf switches. On the other hand, SW#03 to SW#05 are switch devices coupled to the leaf switches and are called spine switches. Packets transmitted by the transmission-side end nodes are transmitted to the reception-side end nodes via the leaf switches and the spine switches.
In the information processing system illustrated in FIG. 34, rate control is carried out in order to suppress retransmission of a packet and so forth due to congestion. FIG. 35 is a diagram for explaining the rate control. The rate control includes flow control by the reception-side end node and congestion control by the transmission-side end node.
In the flow control, the reception-side end node explicitly notifies the transmission-side end node of a receive window (RWIN) indicating the number of packets that can be received by the reception-side end node by an acknowledgement (ACK) about each flow. In FIG. 35, regarding flow #1, the RWIN is three packets because two packets are stored in a receiving buffer 89. Furthermore, regarding flow #2, the RWIN is four packets because one packet is stored in the receiving buffer 89. In FIG. 35, the packet is represented as “ptk.”
It is possible to calculate a theoretical maximum RWIN for each flow from the throughput or round trip time (RTT) of the network. Although the RWIN is represented by the number of packets here, the RWIN may be represented by a data amount such as the number of bytes because the data amount is obtained by multiplying the number of packets by the packet size.
In the congestion control, the transmission-side end node estimates the state of the network, such as congestion, from packet loss or timeout and controls a congestion window indicating the number of packets transmitted to the reception-side end node about each flow. The reception-side end node is not informed of the congestion window and therefore estimates the congestion window by the number of packets per unit time or the like.
In FIG. 35, the transmission-side end node transmits two packets on the basis of the congestion window regarding flow #1 and transmits three packets on the basis of the congestion window regarding flow #2.
In communications using the transmission control protocol (TCP), the flow control and the congestion control simultaneously work and the number of packets transmitted by the transmission-side end node is determined by the smaller window in the RWIN and the congestion window. In general, RWIN congestion window is satisfied. However, if RWIN<congestion window is satisfied, explicit rate control by the reception-side end node is enabled.
A related art is known in which, if handing down to a second communication system of a lower speed is carried out in response to the lowering of the communication quality in communications using a first communication system, the throughput is improved by reducing a reception widow size notified to the communication counterpart.
Furthermore, a related art is known in which, in the case of transmitting packets from a first transmission section to a second transmission section with larger transmission delay, the lowering of the transmission efficiency due to congestion of the second transmission section is suppressed by increasing or decreasing the maximum amount of data that can be transmitted on the basis of the round trip time of the second transmission section.
Moreover, a related art is known in which the throughput is improved by collecting parameters such as the round trip time, the path maximum transmission unit, and the line speed and calculating the optimum window size of file transfer on the basis of the parameters.
In addition, the following related art is known. For example, the time is divided into two slots. In a first slot, the throughput is estimated. In a second slot, rate adjustment is carried out for each flow on the basis of the ratio between the estimated throughput and an expected throughput of the case in which only the reception side is subject to limitation.
As one example of related arts, Japanese Laid-open Patent Publication No. 2011-176540, Japanese Laid-open Patent Publication No. 2003-32295, Japanese Laid-open Patent Publication No. 2001-195326, and Haitao Wu, Zhenqian Feng, Chuanxiong Guo, Yongguang Zhang, “ICTCP: Incast Congestion Control for TCP in Data Center Networks,” ACM CoNEXT 2010, Nov. 30-Dec. 3 2010, Philadelphia, USA are known.